Seat occupancy sensors are commonly used in automotive vehicles for purposes of airbag control or other applications. In general, seat occupancy sensors present a plurality of switching elements, arranged in an array configuration and distributed over the surface of the vehicle seat. The individual switching elements are typically configured as simple on/off switches or as pressure sensing elements, e.g. force sensing resistors, in which, above a certain threshold force, an electrical resistance continuously varies with the force acting on the seat.
In a possible application of those seat occupancy sensors, an actual seat occupancy status is determined by means of the seat occupancy sensors and, in case of a car crash situation, the airbags associated with the respective seat are deployed only if the actual seat occupancy status requires such deployment. In a different application, the signal of the seat occupancy sensors are used in a seat belt warning system for generating a warning signal if a specific vehicle seat is occupied and the corresponding seat belt is not fastened.
In order to reliably detect if an occupant exerts a pressure on the seat, the pressure sensors have usually interposed between the seat cushion (of the seating surface or of the backrest) and the seat cover or seat trim to detect the occupancy state of a vehicle seat. If the seat is also equipped with a seat heater, the pressure sensor is usually arranged beneath the seat heater, i.e. between the seat heater layer and the seat cushion.
Now a considerable number of seats are manufactured by gluing the trim and/or the seat heater layer to the underlying seat cushion. In this case, the seat heater layer, if required, and the trim are assembled onto the seat cushion together with a thermosettable bonding agent between the different layers. The assembly is subsequently subjected to heating and pressure in order to activate the glue and to bond the different layers together substantially on their entire surface.
During this thermosetting stage, a pressure sensor arranged below the trim or immediately below the heater layer is exposed to rather harsh conditions which may damage the pressure sensor. Furthermore, once the assembly is set, the pressure sensor is fixedly located and may thus no longer adapt its position to a deformation of the seat caused by an occupant.